As a disk device, a magnetic disk drive is known, which comprises a housing including a base and a top cover and accommodating therein a rotatable magnetic disk and an actuator which supports a magnetic head. Further, such a method of improving the performance of a disk drive has been proposed, that the housing is sealed with a low-density gas such as helium so as to reduce the rotation resistance of the magnetic disk and the magnetic head.
In such a magnetic disk drive, the top cover is jointed to the base of the housing by laser welding to form an enclosed housing and increase the airtightness of the housing. The laser welding is carried out on along an entire outer circumference of the top cover. Here, in order to obtain high airtightness, it is necessary to maintain a stable welding quality all around the circumference.
In the above-described disk drive, the welded portion between the base and the cover is formed along the outer circumference of the cover, and thus the welded portion is uncovered to the surrounding of the device. When handling the disk drive, for example, when the disk drive is inserted to or removed from the support rack, the welded portion may be brought into contact with the support rack. In order to prevent the fracture of the welded portion by such contact, the strength of the welded portion should preferably be enhanced.